Does it ever end? I had all the upgrades by wave 20 and after that I just held the mouse button down and the enemies barely even made it onto the screen. Played til wave 31 just to see if anything else happened, then gave up. Just seems FAR too easy to be worth bothering with.
Didn't see the point of the human defenders - just used the fist attack for the first few levels until the upgrades started piling up and then I didn't even need to use that, just held down fire and obliterated everything. No new enemies after the first 10 waves or so, didn't seem any point continuing.
Could be interesting if you tweak it a bit though.